Mined payloads, such as various metal ores, are typically transported above ground or through the tunnels of an underground mine by either a railway trains including a locomotive and one or more cars operating on a fixed system of railway tracks, or rigid body, load-carrying trucks. Although each known system may be advantageously utilized in certain applications, they are both subject to various disadvantages.
A railway system, especially one underground, is relatively expensive to install and operate due to the cost of acquiring the locomotive and installing the fixed railway system and the associated maintenance costs. Furthermore, and perhaps more importantly, an underground railway system is route-specific and therefore not flexible to changes in route without incurring the expense of installing additional railway tracks. Underground mines typically have several mining areas, which may occur on multiple levels within the mine. The mined product, such as ore, is typically transported from each mining area to a common receiving area, and then through one or more vertical chutes connecting different levels of the mine if required, to a central processing area where the ore is processed, or sufficiently crushed. The ore is then typically removed from the mine through a single vertical shaft extending to the surface. A single ore crusher and associated shaft is typically used due to the prohibitive costs associated with drilling a shaft from the surface to the mining area deep below the ground. As each new mining area opens, it is necessary to incur the cost of installing new track for the railway system, or to use supplemental vehicles to haul the ore from the mining area to the end of the railway track system.
Rigid body load-carrying trucks, such as wheeled dump trucks, are not route-specific since they are capable of traveling over various roadways within the mine between various origination and destination points. However, known trucks of this type are typically designed for hauling loads over relatively short distances and rough terrain, such as that which may be experienced in above ground applications. Accordingly, such trucks are typically designed with relatively large tires for relatively slow speed operation and are relatively expensive to operate and maintain due to fuel and tire costs. The efficiency of these vehicles typically decreases as the hauling distance increases. In addition, a single rigid body truck of this type has a significantly lower payload capacity as compared to the multi-combination vehicle of the present invention. They are therefore not suitable for hauling ore great distances away from the mine, limiting the distance that ore can be transported to a local processing plant at reasonable cost.
Another difficulty with these types of dump trucks are that the roads constructed in underground mines are typically blacktop roads that are not designed to carry excessive loads. Wheeled dump trucks with large tires carry a significant loading per axle, up to 33 tons per axle, and are prone to tearing up of blacktop roads, thereby precluding their use. In lieu of blacktop roads, clay and gravel roads are used that must be grated and treated with water for safety purposes, i.e. to keep down dust from the road. Other problems with articulated dump trucks are that they have poor power-to-weight ratios and, with low engine efficiency, a significant amount of hot air per ton of ore hauled is exhausted into the mine. Cold ventilation air has to be continually pumped into the mine via ventilation shafts. One of the major costs in establishing underground mines is thus the construction and drilling of ventilation shafts. The excess heat produced by dump trucks means that the time that they can operate underground is limited. Since the dump trucks move relatively slowly, and the inclination within underground mines is usually constant, the depth of mine accessible by these dump trucks is limited, typically to a depth of up to six hundred meters.
Multi-combination vehicles, such as over-the-road vehicles, are known and include a prime mover coupled to a plurality of trailers and converter dollies. Typically these vehicles have a single power source, generally a diesel engine, and are limited in gross combination mass to 200–230 tons. These multi-combination vehicles, commonly referred to as “road-trains” have been in use for some time, particularly in Australia, for the purpose of hauling mined products, or the commodities of other industries, over above ground roadways. Conventional “road-trains” are typically designed for use at relatively high speed and on relatively flat ground, and are therefore not capable of hauling loads out of underground mines for the following reasons.
Due to the heavy loads of the road-train combination, the traction provided by the wheels of a road-train, usually provided to two rear axles, is insufficient for any realistic gradient found in underground mine roads. Alternatively, the roads from underground mines would have to be constructed at a much gentler slope leading to excessively long tunnels. In addition, the relatively low speed of the road-trains underground due to the size of the tunnels and safety considerations result in road-trains traveling underground for a significant length of time, even up to an hour in some cases. This places strain on the road-train cooling system that is typically designed for road-trains traveling at significant speeds, generally more than 80 km/h and the engines generally overheat.
There have been several proposals in relation to vehicles where there is an increase in its traction, including hydraulically driven axles and mechanically linked axles while using a single power source. Other proposals have included the use of a separate engine placed on the dolly or trailer that assists in pulling the load. Although vehicles having a trailer with an additional engine are known, these have been found to be useful only for providing short term bursts of power to the road-train as a whole and are not suitable for long-term hauling especially out of underground mines for the following reasons. Firstly, the additional engines are mounted on top of the trailer or dolly, reducing the usable volume of the road-train for ore or load carrying. Secondly, these additional engines are not accommodated within the existing chassis structure of current road-trains and are therefore not road-legal. Furthermore, and perhaps most importantly, these additional engines once again have standard cooling mechanisms that have been found to be insufficient when the road-train has been traveling up a gradient for a relatively long time at a relatively slow speed. Even if a road-train having a single power source was used on flat roads within the underground mine, the slow speed that the vehicle is limited to travel results in the road-train's engine overheating.
Multi-combination vehicles for dedicated road haulage tasks, such as mineral concentrate haulage, are currently operating at Gross Combination Mass (GCM) up to 230 tons. However, there is a practical limit to the GCM of the multi-combination vehicle with a single prime mover. The cost of haulage is determined mainly on weight. If one can therefore increase the total haulage that can be moved by a single prime mover that does not require additional operators, the cost benefit is substantial, especially if ore can be hauled directly from within a mine without needing to be reloaded onto another transport system.
The inventor is unaware of any known above-ground or under-ground, road-legal multi-combination vehicle of the type just described, which is capable of gaining access to an underground mine and operating within the profiles of the mine as typically exists in underground mines throughout the world. The inventor is further unaware of any above ground road-legal multi-combination vehicle that is capable of operating normally without unnecessarily loading the primary engine of such vehicles.
In view of the foregoing disadvantages and limitations associated with known load-carrying vehicles, a commercial need exists for an improved load-carrying vehicle for use both above ground and in underground mines that overcomes at least some of the abovementioned problems or provides the public with a useful alternative.
Accordingly, the present invention discloses an additional motive power source for use with a prime mover, advantageously located within the chassis of a trailer and including a unique cooling mechanism that enables operation of the road-train at low speeds and steeper gradients than hitherto known.